The present invention relates to a method and apparatus for use in optometric examinations of video display terminal users.
An increasing number of people spend many hours a day looking at a video display terminal (VDT), such as a computer screen monitor. Whether used for business, entertainment, pleasure, research, or other reasons, prolonged time spent focusing on a VDT screen can lead to considerable eye strain. As the use of VDTs becomes even more widespread, so too does the number of ophthalmological afflictions caused by their use. These afflictions are often manifested as headaches, neck or shoulder pain, tired eyes, color fringes, blurred vision, double vision, changes in spectacle prescription over time, or loss of focus. The alphanumeric and graphic character images comprising VDT images are made up of pixels that do not have clearly defined borders. The eye muscles of accommodation constantly try to bring these images into focus, causing strain on the eyes.
VDT users typically maintain a constant distance of approximately 40-60 centimeters from a VDT. The constant distance forces prolonged use of the same eye muscles, resulting in significant amounts of stress and fatigue on the eyes. These characteristics of VDT use, aggravated by the many hours that VDT users spend looking at VDTs, cause peculiar eye problems requiring prescription spectacles specifically selected to treat and prevent the afflictions of VDT users.
To determine an effective prescription for VDT users, test equipment and procedures must be implemented to simulate actual use of a VDT. A prescription for reliable corrective lenses cannot accurately be determined without examining the eyes under conditions that accurately simulate those encountered by VDT users.
The traditional process used by medical practitioners to assess the need for corrective lenses involves placing an apparatus in front of the patient that enables the doctor to change lenses while simultaneously asking the patient to choose which lens performs the best. As the doctor changes lenses, the patient looks through the apparatus to focus on a test image. Through essentially a trial and error process, the doctor determines a combination of lenses and a prescription that provides the greatest relaxation for the eye muscles. However, if the image upon which the doctor has the patient focus does not accurately simulate the actual conditions the patient experiences, the prescription cannot be determined reliably. Traditional forms of testing equipment, including nearpoint cards and projections on walls, do not provide satisfactory simulation of actual conditions for VDT users. A doctor is reduced to essentially making an educated guess as to the prescription, letting the patient use the prescription spectacles to determine if they are satisfactory. If they are not satisfactory, the patient then has to return to the doctor and the process is repeated until a satisfactory prescription is achieved. This process is inefficient, wasting valuable time and energy.
An adequate vision test for VDT users should solve at least three main problems. The first problem is one of providing the doctor flexibility. A vision test must be sufficiently flexible to allow a doctor to examine patients with a wide variety of individual needs. The second problem is one of adequately simulating a VDT. The vision test should accurately simulate the actual work conditions of VDT users. Solving this second problem requires a testing apparatus that forces the patient""s eyes to act as they would when focusing on a VDT. Solving the problem of accurate simulation is made possible if the patient is in the same relative position they would be in when using a VDT (i.e., the same distance from the screen, etc.), and if the test image accurately simulates a VDT display. The third problem that must be solved is the problem of accurate, objective evaluation. Solving this third problem is accomplished though retinoscopy. Retinoscopy involves using a retinoscope objectively to measure the refractive status of the eyes.
To be effective, retinoscopy requires reducing the off-axis angle during the examination. The term xe2x80x9coff-axis anglexe2x80x9d refers to the angle between the line segment from the patient""s eye to the patient""s focal point on the test image, and the line segment from the patient""s eye to the doctor""s retinoscope. This allows the doctor to examine the patient from a point substantially along the line of sight from the patient to the test image. In order to obtain an accurate, objective evaluation of the patient""s eyes, the doctor""s retinoscope should be within approximately one inch of the test image. Using the retinoscope at a location that provides a small off-axis angle is what allows for an objective evaluation of the patient""s prescription needs. If the off-axis angle is too large, the doctor cannot use the retinoscope for an objectively accurate evaluation. The alternative is the subjective process of having the patient try test lenses and report which prescription functions the best. This subjective evaluation does not afford the same accurate results as the objective evaluation though proper use of a retinoscope at a reduced off-axis angle.
Vision testing systems currently available do not provide an economical, reliable, compact, or simple-to-use solution to all three of these problems. Even existing systems designed specifically for conducting optometric exams on VDT users do not completely solve the problem of adequate simulation. Although they do place the testing screen a distance from the patient that represents VDT use, they do not provide the most accurate simulation of a modern, high-resolution VDT display. Examples of such systems include those represented by U.S. Pat. Nos. 4,576,454; 4,998,820; 5,191,367; and 5,325,136.
One of the biggest limitations on previous eye-testing systems is that they provide little flexibility for doctors to meet patient needs. They are limited to one static, fixed image. Most VDT users are subject to continually changing images, constantly forcing the eye to refocus on new characters. Without being able to change an image, a doctor cannot accurately simulate actual VDT use. Using one static image also prevents efficient testing of VDT users who have special needs, such as children or others who do not read well, and people whose reading proficiency is in another language. To accommodate such users would require physically changing the actual apparatus and substituting it with another specialized apparatus specifically designed to accommodate that patient""s needs. In addition to the time wasted physically switching apparatuses, a doctor would have to purchase, maintain, and store as many different types of apparatuses as necessary to meet the individual needs of patients. To do so, a doctor would incur significant expense and inconvenience.
While there are vision testing apparatuses that use computer screens (and therefore accurately represent the display of a VDT), those systems are not specifically designed to determine prescriptions for use with VDTs, and they do not simulate actual working conditions of a VDT user. One such system is the AcuityMax computer software program produced by Science20/20. That product is not cost effective because it requires a dedicated computer (or the manufacture will not guarantee support). Accordingly, a doctor is forced pay for an entire computer system for the sole purpose of testing vision. Also, that product is not designed to test VDT users for the purpose of determining a prescription for use with a VDT. AcuityMax is only used in acuity testing to take the place of a standard acuity projector. It is used at a distance of 8 to 24 feet from the patient, not at a distance representative of VDT use. Because the software allows a computer to replace an acuity projector, rather than using the computer to adequately simulate a VDT work environment, it is ineffective in solving the problems encountered in deriving an effective prescription for VDT users.
Therefore, it is the object of the present invention to provide an improved method and apparatus for examining the eyes of VDT users. The present invention provides doctors a more flexible, realistic, and accurate system for determining the best prescriptions for VDT users.
As illustrated through one embodiment, the present invention generally comprises a vision testing method and apparatus for use in optometric examinations to simulate the actual conditions encountered by a VDT user and to facilitate prescribing corrective lenses that will perform well for a patient using a VDT. The invention is economical, reliable, compact, and simple to operate. One feature of this invention solves the problems of providing doctors flexibility and accurately simulating a VDT display by implementing a programmable digital display screen. As used throughout this specification and the attached claims, the phrase xe2x80x9cdigital display screenxe2x80x9d refers to electronic display mechanisms including, without limitation, liquid crystal display (LCD), gas plasma, cathode ray tube (CRT), and others known in the field of digital displays. Also, as used throughout this specification and the attached claims, the term xe2x80x9cdoctorxe2x80x9d refers to anyone using an embodiment of this invention for optometric examinations. The terms xe2x80x9cpatientxe2x80x9d or xe2x80x9cVDT userxe2x80x9d refer to anyone being examined through an implementation of this invention.
This invention affords a doctor significant flexibility by using a programmable digital display screen. The programmable digital display screen enables the doctor to select an image based on a particular patient""s needs. Also, because a digital display screen is made up of pixels that present an approximately Gaussian light distribution, the digital display screen provides viewing conditions virtually identical to those experienced in the particular work environment of the VDT user. This characteristic affords an extremely accurate simulation of typical VDT user eye strain, and it does so in the controlled environment of the doctor""s preferred examining location. Of course, to be an effective testing tool, the off-axis angle must be reduced as much as practicable so that the doctor can examine the patient from a point substantially along the line of sight from the patient to the digital display screen. Also, the distance from the patient to the digital display screen must be representative of the distance from the patient to the VDT under typical use. One implementation of this invention includes situating a patient a representative working distance from a desktop, laptop, or palmtop computer screen (or from any other device having a digital display screen). While having the patient focus on images on the computer screen, the doctor can use a retinoscope to evaluate the patient""s focusing response from a point substantially along the line of sight from the patient to the digital display screen.
Although using a desktop, laptop, or palmtop computer represent alternative embodiments of this invention, they are not preferred embodiments. A preferred embodiment includes a vision tester apparatus with a programmable digital display screen specifically for use in practicing the invented method in an economical, reliable, compact, and simple-to-operate form.
In a preferred embodiment, the vision tester can display text and graphical images that are either pre-stored in the vision tester or sent from a computer to the vision tester during the examination. The vision tester can include a light source that illuminates the digital display screen, and the digital display screen can be either a monochrome or a color display. The pixel pitch of the digital display screen can be selected to match the viewing conditions of any type of VDT. Furthermore, textual images can display characters in a variety of type fonts and styles used by VDTs. Because this invention uses a digital display screen, the pixels comprising images used in conducting the vision exam exhibit an approximately Gaussian light distribution virtually identical to that experienced by a patient using a VDT in that patient""s work environment. Accordingly, unlike with prior vision testers, an embodiment of this invention requires no special construction or components or design in order to diffuse the light to create an approximately Gaussian pattern artificially.
The digital display screen is driven by digital display screen control electronics. The control electronics provide timing and color data to the digital display screen and act as an interface to a frame buffer. The frame buffer holds images that are to be displayed on the digital display screen during operation of the system. These images can consist of any appropriate mix of text and graphics. The graphics can include pictures without accompanying text for allow examination of young patients or patients who do not read well. Furthermore, text images can be in any language. The images to be displayed can be stored in several different forms including pre-loaded ROM, or RAM that is driven from a computer input device. The image to be displayed is determined by the doctor.
A computer input device can connect a computer to the vision tester by any number of methods currently know in the computing art, including, without limitation, standard VGA cables or any of several digital interfaces now being supplied on the market. Microcontroller electronics control the operation of the unit. In the simplest form, the microcontroller electronics could include FPGA that reads control switches to take appropriate action (such as displaying a particular image or dimming a display). In a more versatile form, the microcontroller electronics could include a microprocessor and appropriate RAM and ROM. The microcontroller electronics send a signal to the frame buffer to select a display image, to the backlight to set a dimming level, and to the computer input device to facilitate the computer interface operation. The doctor has controls to turn the system on or off, select the desired image, and control the brightness of the digital display screen. These controls can include switches on the vision tester, or they can be on a connected computer.
The vision tester can be powered through various mechanisms. One example would include either a disposable or rechargeable battery unit. The vision tester can be constructed so that a rechargeable battery unit can either be removed from the vision tester for charging or charged while still inside the vision tester. Another example of a power source would include a plug for connecting the vision tester directly to a wall outlet.
A vision tester embodying this invention also solves the problem of accurate examination by allowing a doctor to reduce significantly the off-axis angle and examine a patient from a point substantially along the line of sight from the patient to the digital display screen. In the case of a computer screen, this could be accomplished by selecting a computer screen with a sufficiently small border. In a preferred embodiment, this is accomplished by constructing the vision tester specifically to reduce the distance between the test image and the position at which the retinoscope is placed to examine the patient""s eyes. One such construction provides an aperture within the digital display screen through which the doctor can examine the patient""s eyes. As used in this specification and the attached claims, xe2x80x9caperturexe2x80x9d is broadly defined as a space through which a doctor can view the patient. An aperture can be a physical hole through the vision tester, a transparent section in the vision tester, or an indentation in the side of the vision tester, such as a recess or sight.
Additional objects and advantages of this invention will be apparent from the following detailed description of a preferred embodiment thereof which proceeds with reference to the accompanying drawings.